Cox Inhibitors
Cyclooxygenases play an essential role in prostaglandin synthesis. Cyclooxygenase-1 (COX-1) is constitutive and relatively long-lived, whereas cyclooxygenase-2 (COX-2) is inducible and relatively short-lived. COX-1 is thought to be responsible for maintaining basal level prostaglandin production, which is important for normal gastrointestinal and renal function. COX-2 is induced by certain inflammatory agents, hormones, growth factors, cytokines, and other agents. COX-2 plays a significant role in prostaglandin synthesis within inflammatory cells such as macrophages and monocytes, and prostaglandin production associated with COX-2 induction can have a deleterious effect on the body. Thus, to reduce unwanted inflammation and to treat certain other conditions, it can be desirable to inhibit COX-2 activity without significantly inhibiting COX-1 activity.
Many non-steroidal anti-inflammatory drugs (NSAIDs) inhibit both COX-1 and COX-2. These non-selective inhibitors include indomethacin (Shen et al. 1963 J Am Chem Soc 85:4881; 4-chlorobenzoyl-5-methoxy-2-methyl-1H-indole-3-acetic acid). It is desirable to identify NSAIDs that inhibit COX-2 activity, but do not significantly inhibit COX-1 activity at physiological levels where COX-2 activity is significantly inhibited. Such selective inhibitors are expected to have the desirable anti-inflammatory, anti-pyretic, and analgesic properties associated with NSAIDs, while having reduced or no gastrointestinal or renal toxicity.
Subsequent to indomethacin administration, the unchanged parent compound, the desmethyl metabolite (O-desmethylindomethacin; (1-(4-chlorobenzoyl)-5-hydroxy-2-methyl-1H-indol-3-yl]acetic acid), the desbenzoyl metabolite (N-deschlorobenzoylindomethacin; (5-methoxy-2-methyl-1H-indol-3-yl)acetic acid) and the desmethyl-desbenzoyl metabolite (O-desmethy-N-deschlorobenzoylindomethacin; (5-hydroxy-2-methyl-1H-indol-3-yl)acetic acid) can be found in plasma in significant amounts (Strachman et al. 1964 J Am Chem Soc 8:799; Helleberg 1981 Clin Pharmacokinet 6:245), all in an unconjugated form (Harman et al. 1964 J Pharmacol Exp Therap 143:215). It has been reported that all three metabolites are devoid of anti-inflammatory activity (Helleberg 1981 Clin Pharmacokine. 6:245 and Duggan et al. 1972 Pharmacol and Exp Ther 181:562), although it has also been reported that the desmethyl metabolite has some ability to inhibit prostaglandin synthesis (Shen et al. 1977 Adv Drug Res 12:90).
Indomethacin derivatives in which the benzoyl group has been replaced by a 4-bromobenzyl group of the acetic acid side chain has been extended exhibit greater selectivity for inhibition of COX-2 relative to COX-1 (Black et al. 1996 Bioorganic & Medicinal Chem Lett 6:725 and Black et al. 1997 Advances in Experimental Medicine and Biology 407:73). In addition, synthesis methodology has been demonstrated for the preparation of indomethacin analogues, some of which do not inhibit cyclooxygenases (Touhey et al. 2002 Eur J Cancer 38:1661).
FAAH Inhibitors
Many fatty acid amides are known to have analgesic activity. A number of fatty acid amides (e.g., arachidonyl amino acids and anandamide) induce analgesia in animal models of pain (see, for example, Walker et al. 1999 Proc Natl Acad Sci 96:12198, Fride and Mechoulam 1993 Eur J Pharmacol 231:313). Anandamide and certain other fatty acid amides (e.g., N-palmitoyl ethanolamine, n-oleoyl ethanolamide, oleamide, 2-arachidonoylglycerol) are cleaved and inactivated by fatty acid amide hydrolase (FAAH) (Deutsch et al. 2003 Prostaglandins Leukol Essent Fatty Acids 66:201; and Cravatt and Lichtman 2003 Current Opinion in Chemical Biology 7:469).
Inhibition of FAAH is expected to lead to an increase in the level of anandamide and other fatty acid amides. This increase in fatty acid amides may lead to an increase in the nociceptive threshold. Thus, inhibitors of FAAH are useful in the treatment of pain. Such inhibitors might also be useful in the treatment of other disorders that can be treated using fatty acid amides or modulators of cannabinoid receptors (e.g., anxiety, eating disorders, and cardiovascular disorders). NPAA (N-palmitoylethanolamine acid anhydrolase) is a hydrolase that breaks down N-palmitoyl ethanolamine (PEA), a fatty acid amide. PEA is a naturally occurring substrate for the cannabinoid receptor 2 (CB2 receptor). Inhibition of NPAA may lead to increased PEA levels. Accordingly, NPAA inhibitors may be useful in the treatment of inflammation and nociceptive pain control. Monoacylglycerol lipase (MAGL, MGL) is a hydrolase which degrades the endocannabinoid ligand, 2-arachidonoylglycerol (2-AG). Although FAAH can also degrade 2-AG, MAGL is believed to be the main enzyme responsible for 2-AG metabolism in the brain. Thus 2-AG inhibitors may be useful in the treatment of cannabinoid receptor related therapies including anxiety, eating disorders, and cardiovascular disorders. Inhibitors of MAGL and FAAH are thought to have various therapeutic uses. Bahr et al. Expert Opin Investig Drugs—2006 Volume: 15 p. 351-65.
In addition, there is evidence (see, e.g., Weber et al. 2004 J. Lipid Res. 45:757) that when FAAH activity is reduced or absent, one of its substrates, anandamide, acts as a substrate for COX-2 that can be converted to a prostamide. Thus, certain prostamides may be elevated in the presence of an FAAH inhibitor. Given that certain prostamides are associated with reduced intraocular pressure and ocular hypotensivity, FAAH inhibitors may be useful agents for treating glaucoma.
CRTH2 Modulators
CRTH2 is a Gai protein-coupled receptor that is thought to be involved in both mediating PGD2-induced chemoattraction and in activation of specific cell types involved in allergic inflammation. It has been reported that CRTH2 is expressed by Th2 cells, eosinophils and basophils, but not by Th1 cells, B cells or NK cells. (Nagata et al. 1999 FEBS Letters 459:195-199).
PGD2 is produced by allergen-activated mast cells and has been implicated in various allergic diseases as a pro-inflammatory mediator, although it may have anti-inflammatory activity in certain situations (Ajuebor et al. 2000 Am J Physiol Gastrointest Liver Physiol 279:G238-44). CRTH2 receptor is a high affinity receptor for PGD2 as is DP-1, a GaS protein-coupled receptor.
CRTH2 agonists activate eosinophils, basophils and Th2 cells in vitro, resulting in induction of actin polymerization, calcium influx, CD11b expression and chemotaxis (Monneret et al 2003 J Pharmacol Exp Ther 304:349-55). An in vivo study has demonstrated that injection of a CRTH2 agonist can elicit transient recruitment of eosinophils from bone marrow into the blood (Shichijo 2003 J Pharmacol Exp Ther 307:518-525). A genetic study of African American and Chinese cohorts found that polymorphisms in CRTH2 were tightly associated with asthma susceptibility (Huang et al. 2004 Hum Mol. Genet 2791). It has been suggested that modulators of CRTH2 may be useful in the prevention and/or treatment of allergic asthma and other allergic disorders (US 2002/0022218 A1 and WO 03/066047). Recruitment and/or activation of eosinophils, basophils and Th2 cells is a prominent feature of the changes that occur in the asthmatic lung. Similar activation of these cell types, or subsets thereof, are believed to play an important role in the etiology of other diseases, including eosinophilic esophagitis and atopic dermatitis (Arora and Yamakazi 2004 Clin Gastroenterol Hepatol 2:523-30; Kiehl et al. 2001 Br J Dermatol 145:720-729). This fact, combined with the fact that CRTH2 mediates PGD2-induced chemotaxis, suggests that compounds that alter chemotaxis by modulating CRTH2 activity could be useful in controlling chronic airway inflammation, atopic dermatitis, chronic obstructive pulmonary disease (COPD), and/or eosinophilic esophagitis. Compounds that alter chemotaxis by modulating CRTH2 activity could also be useful in controlling allergic rhinitis. Allergic rhinitis is classified as either seasonal (SAR) or perennial (PAR) depending upon the type of trigger and duration of symptoms. SAR symptoms occur in the spring, summer and/or early fall and can be triggered by outdoor allergens such as airborne tree, grass and weed pollens while PAR is usually persistent and chronic with symptoms occurring year-round and is commonly associated with indoor allergens such as dust mites, animal dander and/or mold spores. Symptoms of allergic rhinitis may include runny nose, nasal itching, sneezing, watery eyes and nasal congestion. CRTH2 modulators may be useful for treating SAR and/or PAR.
CRTH2 antagonists that reduce the ability of Th2 cells and eosinophils to respond to mast-cell derived PGD2 could be useful for preventing and/or treating allergic disorders such as allergic rhinitis and asthma.
It is often found that agonists induce desensitization of the cell system by promoting internalization and down regulation of the cell surface receptor (Int Immunol 15:29-38, 2003). Therefore, certain CRTH2 agonists may be therapeutically useful because they can cause the desensitization of PGD2-responsive cells. It has been shown that certain CRTH2 agonists can induce desensitization of PGD2-responsive cells to subsequent activation by a CRTH2 agonist (see, e.g., Yoshimura-Uchiyama et al. 2004 Clin Exp Allergy 34:1283-1290). Importantly, CRTH2 agonists may also cause cross-desentization. Cross-desensitization, which can occur in many cell-signaling systems, refers to a phenomena whereby an agonist for one receptor can reduce or eliminate sensitivity of a cell type to an unrelated agonist/receptor signaling system. For example, it is known that treatment with the CRTH2 agonist indomethacin reduces expression of CCR3, the receptor for the chemoattractant, eotaxin (Stubbs et al. 2002, J Biol Chem 277:26012-26020).
DAO Inhibitors
It has been suggested that certain inhibitors of D-amino acid oxidase (DAO), including certain heterocylic-2-carboxylic acids, might be useful for improving memory, learning and cognition in patients suffering from neurodegenerative disorders US20030162825). Indomethacin has also been shown to be an inhibitor of DAO (Chen et. al 1994 Drug Metabol Drug Interact. 11:153-60). DAO degrades D-serine and other D-amino acids. D-glutamate and D-serine are thought to be agonists of N-methyl-D-aspartate (NMDA)-glutamate receptors that mediate a wide variety of brain activities, including the synaptic plasticity that is associated with certain types of memory and learning (US20030162825). Thus, it is thought that inhibition of DAO will lead to increased D-serine levels and improved cognitive function.